1. Field of the Invention
The present invention relates to a ceramic material useful for optical fiber connector member, and to a optical connecting member, particularly, to a ferrule using the ceramics for holding optical fibers. The present invention relates to a method of producing zirconium ceramic material and, particularly, an optical fiber connector member using the same.
2. Prior Art
Recently, optical communication systems have been widely utilized in the world with an increase in an amount of communication. In the field of the optical communication, optical fiber connector members are used to connect one fiber to the other mechanically and optically.
For the optical connector member, as shown in FIGS. 1 and 3, a pair of ferrules 1 and 1 are used, each which has a through hole along the axis thereof, and a rear end of the ferrule is held in the backing body 2 or a flange member. Each end portion of a pair of two optical fibers to be connected is inserted through the hole and adhered to inner surface of the ferrule, of which the optical end surface is adjusted so as to form a face with together an end face of the ferrule. The end surfaces of a pair of ferrules with the fibers, as shown in FIG. 3, are abutted to each other using a appropriate casing to form an optical connector. In some cases, a ferrule is connected to another ferrule fixed to a package which contains an optical device to optically connect the fiber to the optical device.
As ferrule materials, metal, ceramics, glass, and plastics have been utilized, but the ceramics is most desirable to be used. The ceramics can be formed with high formation accuracy to precision tolerances below 1 xcexcm of inner and outer diameters, and have low friction constant, so that the fibers may easily be inserted to and fixed in the through hole. Also, the ceramics has high hardness, high wear resistance and low heat expansion coefficient so as to be steady with regard to application of outer stress and quick change in temperature.
Ceramic material for the connectors has been replaced from conventional alumina based ceramics to zirconia based ceramics which has about one-half of the Young""s modulus of alumina. As a result, the zirconia based ceramics has advantages to enhance capability of attaching the two ferrules with small applied force when they are connected in contact to each other. The Japan patent publication.JP-A 5-333238 discloses zirconia based ceramics for ferrules, which is a sintered zirconia ceramics which partially stabilized by about 3 mol % of yttria Y2O3, to increase thermal strength property.
The application ranges of the optical fiber connectors have been recently expanded so that the connectors are required to exhibit more durability for using as optical fiber connectors.
For example, optical fiber communication lines, including such optical fiber connectors, have been located for a long time in severe circumstances at high temperature and humidity, such as in deserts or abysses. In these cases, it requires that the materials for the connectors do not decrease in connecting properties even over time without being exchanged, and is usable in a longtime steady state.
However, Y2O3-partially stabilized zirconia based ceramics as mentioned above have a problem of reducing its properties while exposed in high temperature and humidity circumstances by transform its tetragonal crystal to monoclinic crystal. In the case of ferrules using such zirconia ceramics, the roughening and deformation are apt to occur on the ferrule surface while they are being held in the hot and wet circumstances, then causing loss of light transmitting through the fibers with connecting defect to the ferrules. It has been understood that these surface defects are due to transformation of the ceramic crystal to monoclinic system and to hydration of the surface layers in high temperature and humidity, then to expand the ferrule tube.
Furthermore, ferrules comprising zirconia ceramics often show black flecks of 1 to 5 xcexcm in size on their surfaces.
For the optical connector devise, a plug is composed from a ferrule which provided with a backing body or a flange 2 on the outer periphery and a fiber in the through hole, composes a plug. Actually, as shown in FIGS. 9 and 10, the two plugs to be connected are inserted in a adapter 32 like a sleeve from both the sides and connected by abutting the optical end surfaces of the fibers in the ferrules of the plugs. Then, the light signal information transfers from the one fiber to the other through the connector.
The ferrule is fabricated so accurately that the center of the hole desired to be located in the center of the ferrule, but it is difficult to center the fiber to the ferrule and to avoid decentering below 1.4 xcexcm between the axes of the fiber and ferrule.
It has been observed that there often is of local difference between centers of a ferrule and a through hole which is bored in the ferrule. This axial divergence causes a loss of light transmission when the light is passed through to the connected fiber ways. Even If the fiber decenters in the ferrule, the two fibers in the ferrules can be aligned to adjust the decentering directions of each fiber on the end surface, allowing the connector to reduce in light transmission loss.
For this purpose, for example, as shown in FIGS. 13A and 13B, a ferrule 1 is formed with four lateral grooves 2c on an outer periphery of its flange 2 at a mutual angle of 90xc2x0 to the axis, and, on the other hand, the plug housing 4 is formed with four corresponding projections 4a on its inner periphery, which can be engaged to the grooves 2c by rotating the ferrule by said angle 90xc2x0 to the plug housing 4. In such conventional structure of the connector, the ferrule is rotated at every angle of 90xc2x0, while the loss of the light of the connector is being measured, and then at a rotating position to attain a minimum loss, the ferrule is attached to the plug housing 4, thus, performing a optical connector.
However, rotation of the ferrule and measurement of light loss are required at least five times to find out the most appropriate rotating position between the ferrule and the plug housing, so that one has much trouble in the operation needed. Further, the rotating of the ferrule was limited to angle intervals of 90xc2x0, not continuous, and therefore the ferrule could not be adjusted to the most appropriate position for really minimum loss of light transmission.
An object of the present invention is to provide zirconia based ceramic material having longer duration without reducing in thermal and mechanical property in high temperature and humidity circumstances.
Another object of the present invention is to provide a optical fiber connector member for connecting the optical fibers usable in high temperature and humidity circumstances for a long time.
Another object of the present invention is to provide a ferrule and a sleeve thereof used as the optical connector member in high temperature and humidity circumstances over a long period.
Another object of the present invention is to provide a ferrule to be adjustable to the most appropriate position for really minimum loss of light transmission.
Another object of the present invention is to provide a ferrule to be adjusted to the most appropriate position by easier operation for fabricating an optical connector member.
A zirconia based ceramic material of the present invention is stabilized by Y2O3, and is limited to an extremely small amount of impurities causing the phase transformation and/or hydration of the ceramics, then, to prevent degradation thereof. To this end, amounts of SiO2 and TiO2in the ceramics should be reduced to a very low level.
A zirconia based ceramic material of the present invention dose not contain Y2O3 substantially but partially stabilized by metal oxide stabilizers other than Y2O3. In the present invention, degradation due to Y2O3 in the ceramics exposed in such hot and wet circumstances can be effectively prevented.
The ceramics material is used for an optical fiber connector member, including ferrule and sleeve.
The present invention includes the ceramics whose weight increases only slightly while the ceramics being held in high temperature and humidity circumstances over a long period.
Further, the present invention provides proper configuration of ferrules to make the connection between the ferrules easy. Such ferrules have a marker which indicates eccentric direction of a through hole on the top end surface of the ferrule, and the marker is usually formed on the outer periphery of the ferrule.
The ferrule of the present invention is formed with a marker on any periphery of the ferrule which indicates a direction of decentering a through hole on the top end surface.
The ferrule of the present invention may be provided with a flange member, and the marker is formed on any periphery of the ferrule and/or the flange member.
The present invention provides a optical fiber connector comprising a ferrule with a through hole in which a optical fiber is inserted and fixed, a plug housing fixed on the periphery of the ferrule, wherein the marker may be formed on any periphery of the plug housing.
For a optical fiber connector, a pair of ferrules are abutted on the top ends in contact to each other, and adjusted such as match the two marks close to each other, then obtaining minimum loss of the light transmission across the connection.